CILIATES 201 



One really conspicuous way in which the Stentor kinetodesma 

 differ from those of the hymenostomes and Metaradiophrya is 

 that in the heterotrich the kinetodesmal fibrils pass from their 

 kinetosomal origin to the right and posteriad instead of anteriad. 

 Accordingly, the kinetodesmal bundles are heavier at the posterior 

 end of the animal than anteriorly. At some points at least, the 

 outer ends of some sheets within the kinetodesmos appear to be 

 in contact with the pellicle. 



It is noteworthy that in Randall and Jackson's micrograph 

 (their Fig. 17) of a transverse cortical section cut near the adoral 

 zone, where pellicular alveoli are present, a row of four small 

 dense profiles appears in the cytoplasmic ridge to the right of each 

 kinety, in precisely the place where kinetodesmal fibrils are found 

 in the hymenostomes. This micrograph might almost have been 

 taken of Paramecium, the resemblance is so striking. It seems 

 likely that the kinetodesmal fibrils at the anterior end of the kinety 

 start out as conventional hymenostome-type structures and 

 aggregate in ribbons farther posteriad. A somewhat similar 

 phenomenon occurs, it will be recalled, in Metaradiophrya, where 

 posterior kinetodesmal fibrils remain free but anterior ones 

 coalesce. 



In addition to kinetodesma, Stentor possesses a system of 

 longitudinal fibers running parallel to but deeper than the kineto- 

 desma. These are called by Randall and Jackson (1958) the 

 M-bands and by Faure-Fremiet and Rouiller (1958a, 1958b) the 

 endoplasmic myonemes. They are weakly birefringent and 

 probably proteinaceous. In ultrastructure they are finely and 

 rather irregularly filamentous, and like the endoplasmic myonemes 

 of the peritrichs they are penetrated and surrounded by mem- 

 branous vesicles and canaliculi (Fig. 84, PI. XXIII). Filamentous 

 strands interconnect adjacent fibers at irregular intervals and 

 broader ones join them posteriorly.- No connection to any part 

 of the pellicle or to any ciliary organelle is reported, but in living 

 cells they appear to be firmly inserted at the posterior holdfast 

 region. 



All observations to date, made on individuals that are at least 

 semicontracted, indicate that both kinetodesma and M-bands are 

 straight. According to the light-microscope studies of Randall 

 and Jackson the kinetodesma are also straight when superextended, 



